The present invention relates to a method of chlorinating metal-oxygen substances by first coating them with carbon.
It is known to react certain metal oxides, such as those of aluminum, titanium and iron, as well as minerals, e.g. clay, containing these metals and oxygen, with chlorine and carbon. It is possible to supply the chlorine and the carbon in the form of compounds containing the same, for example CCl.sub.4 and CO, as well as in the form Cl.sub.2 and elemental carbon. This reaction is termed a "reduction-chlorination" in the article entitled, "Hydrogen Affinities--A New Ordering of Metals to Accomplish Difficult Separations", by D. F. Othmer and R. Nowak, AIChE Journal, Volume 18, No. 1, pp. 217-220 (January 1972). It is in this sense that the terms "reduction-chlorination" and "reduction-chlorination process" are used herein.
It is known to provide the carbon as a coating on alumina by spraying it at elevated temperatures with a hydrocarbon material, such as fuel oil. See U.S. Pat. No. 3,811,916, issued May 21, 1974, for "Method for Carbon Impregnation of Alumina".
U.S. Pat. No. 2,725,349, issued Nov. 29, 1955, for "Fluid Coking with Alumina Seeds", describes fluid coking techniques using seeds of aluminum oxide. There is a much larger build-up of carbon than in U.S. Pat. No. 3,811,916. The carbon is deposited in a green form containing volatiles, and the resulting particulate, petroleum coke product, is calcined to drive off such volatiles to make the product suitable for use in anodes in the Hall-Heroult cell for the production of aluminum.
U.S. Pat. No. 3,842,163, issued Oct. 15, 1974, for "Production of Aluminum Chloride", discusses the chlorination of alumina in the presence of carbon which has been coated on the alumina particles utilizing techniques as described in U.S. Pat. No. 3,811,916. In this procedure, the alumina has an alpha-alumina content of less than about 5% by weight.
Another chlorination process is that described in U.S. Pat. No. 2,805,120, where coal is used to agglomerate particles of ore to form briquettes. The briquettes are subsequently calcined to remove volatile hydrocarbons before the briquettes are contacted with chlorine for the chlorination step. The use of coal, which also acts as an agglomerating agent to bind the ore particles into briquettes, represents quite a different approach to providing the carbon in reduction-chlorination reactions as compared with the techniques of U.S. Pat. No. 3,842,163, where oil is coked on the ore particles, and U.S. Pat. No. 3,811,916 where both oil and gaseous hydrocarbons are coked on the ore to form individual, carbon-coated particles suitable for chlorination in a fluidized bed reactor.